# Precalculus : Understand features of hyperbolas and ellipses

## Example Questions

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### Example Question #213 : Conic Sections

Which point is one of the foci of the hyperbola ?

Possible Answers:     Correct answer: Explanation:

To find the foci of a hyperbola, first determine a and b, and then use the relationship In this case, the major axis is horizontal since x comes first, so and .

Solve for c: add 9 to both sides take the square root Since the center is and the major axis is the horizontal one, our foci are . The only choice that works is .

### Example Question #214 : Conic Sections

Determine the length of the foci for the following hyperbola equation: Possible Answers:    Correct answer: Explanation: To solve, simply use the follow equation where c is the length of the foci.

In this particular case,  Thus,  ### Example Question #215 : Conic Sections

Find the foci of the hyperbola with the following equation: Possible Answers: and  and  and  and  and Correct answer: and Explanation:

The standard form of the equation for a hyperbola is given by The foci are located at (h+c, k) and (h-c, k), where c is found by using the formula Since our equation is already in standard form, you can see that  Plugging into the formula So the foci are found at AND ### Example Question #216 : Conic Sections

How can this graph be changed to be the graph of ? Possible Answers:

The graph should be an ellipse and not a hyperbola.

The center box should extend up to and down to , stretching the graph.

The -intercepts should be at the points and .

The graph should have -intercepts and not -intercepts.

The -intercepts should be at the points and .

Correct answer:

The -intercepts should be at the points and .

Explanation:

This equation should be thought of as .

This means that the hyperbola will be determined by a box with x-intercepts at and y-intercepts at .

The hyperbola was incorrectly drawn with the intercepts at instead.

### Example Question #217 : Conic Sections

Which of the following would NOT be true of the graph for ?

Possible Answers:

All of these statements are true.

The graph never intersects with the -axis.

The graph opens up and down.

The graph is centered at .

The graph never intersects with the -axis.

Correct answer:

The graph never intersects with the -axis.

Explanation:

The graph should look like this: ### Example Question #121 : Hyperbolas And Ellipses

Which of these equations produce this graph, rotated 90 degrees? Possible Answers:     Correct answer: Explanation:

Rotated 90 degrees, this graph would be opening up and down instead of left and right, so the equation will have the y term minus the x term.

The box that the hyperbola is drawn around will also rotate. It will now be up/down 2 and left/right 3.

This makes the correct equation .

### Example Question #219 : Conic Sections

What is the equation of the conic section graphed below? Possible Answers:     Correct answer: Explanation:

The hyperbola pictured is centered at , meaning that the equation has a horizontal shift. The equation must have rather than just x. The hyperbola opens up and down, so the equation must be the y term minus the x term. The hyperbola is drawn according to the box going up/down 5 and left/right 2, so the y term must be or , and the x term must be or .

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